Second-harmonic-generation (SHG) is a second order nonlinear process induced by the \(\chi ^{(2)}\)  susceptibility tensor of a material, typically a crystal, which converts an electromagnetic wave of frequency \(\omega \)  into a wave at the second harmonic frequency \(2\omega \)  [1]}, [2]}.
Because of the small value of \(\chi ^{(2)}\)  of common nonlinear materials either long device lengths or high light intensities are required to achieve efficient SHG.
